The problem is that your under layment or felt paper more than likely does not have the ability to let the moisture rising up from your appliances taking showers etc...the felt traps the moisture trying to escape so it stays in the attic and due to the humidity the moisture attaches to the nails just like a coke can you take out of the refrigerator and accumulates until dripping down...bigger problem is any moisture that does pass through the nails gets trapped above it because its trapped by the non breathable felt and it fans out on top of the plywood decking under the felt almost like a trash bag on a wrestler tryin to lose weight quickly..they are called cats eyes if there is rot around the nail head inside its way worse on the top side...change your roof and get a system that will address that and increase your ventilation as well

On Friday, January 12, 2018 at 11:11:08 AM UTC-5, wrote:
The problem is that your under layment or felt paper more than likely does not have the ability to let the moisture rising up from your appliances taking showers etc...the felt traps the moisture trying to escape so it stays in the attic

This is an old thread, the OP and there problem is long gone. But since
you re-opened it, if there is excess moisture in that attic, it's not
the underlayment that's the problem. According to the description, the
attic has a ridge vent, continuous soffit vents. That should be enough
to allow proper ventilation through the correct path. Assuming it's
excess moisture and not a roof leak, I'd be looking at why there is too
much moisture in the attic. Are bathroom vents venting into the attic
instead of outside? A dryer hose disconnected and venting in there?
Humidity from a humidifier set too high? No vapor barrier on the insulation
facing the living space?